Organosilane and organosilicone compounds dissolved in organic solvents have been used to render masonry and other substrates water repellent in the past. For example, U.S. Pat. No. 3,772,065 to Seiler discloses a method for waterproofing masonry structures. The method comprises impregnating masonry structures with an alcoholic or hydrocarbon solution of hydrolyzed alkyltrialkoxysilanes and their lower oligomers. European Patent 0 075 962 to Puhringer discloses an impregnating agent for porous building materials containing tetraalkoxysilanes, alkyltrialkoxysilanes, or aryltrialkoxysilanes, a surfactant, an aliphatic solvent, and an optional condensation reaction catalyst. U.S. Pat. No. 4,937,104 to Puhringer discloses a process for imparting hydrophobicity to mineral substrates. The process comprises mixing at least one silane, a hydrolysis product of the silane, a condensation product, or combinations thereof, with a surfactant and a water/organic alcohol mixture. The resulting emulsion is applied to a mineral substrate. However, organic solvents such as alcohols and hydrocarbons are flammable, expensive, and have detrimental environmental and physiological effects.
U.S. Pat. No. RE 33,759 to DePasquale et al. discloses an aqueous emulsion containing silanes for rendering masonry surfaces water repellent. The system consists essentially of a hydrolyzable silane, and oligomers thereof; a surfactant having hydrophilic-lipophilic balance (HLB) of 4 to 15; and water. The hydrolyzable silane has the formula R.sub.n SiR'.sub.(4-n) where n is 1 or 2, R is independently selected from hydrocarbon and halogenated hydrocarbon groups of 1 to 20 carbon atoms, and R' is selected from alkoxy groups of 1 to 3 carbon atoms, halide groups, amino groups, and carboxyl groups. The surfactant can be nonionic, amphoteric, ionic, or combinations thereof. The preferred surfactants are SPAN.RTM. surfactants, which have HLB values in the range of 4.3 to 8.6, and TWEEN.RTM. 61 and TWEEN.RTM. 81, which have HLB values of 9.6 and 10.0, respectively. However, pH and particle size of the emulsion are not disclosed. Particle size change with time is not disclosed.
U.S. Pat. Nos. 4,877,654 and 4,990,377, both to Wilson et al., disclose aqueous emulsions for rendering porous substrates water repellent. The emulsion comprises a hydrolyzable silane, an emulsifier with HLB of 1.5 to 20, a buffer, and water. The silane has formula R.sub.n SiR'.sub.4-n, where R is independently selected from hydrocarbon- and halogenated hydrocarbon groups of 1 to 30 carbon atoms; n is 1 or 2, and R' is an alkoxy group of 1 to 6 carbon atoms, a halide group, an amino group, or a carboxyl group. Nonionic, cationic, anionic, and amphoteric emulsifiers are suitable. The emulsion has a pH of 6-8. However, stability and particle size of the emulsion are not disclosed. Particle size change with time of the emulsion is not disclosed.
U.S. Pat. No. 5,226,954 to Suzuki, discloses an organosilicon composition comprising a monoalkyltrialkoxysilane and/or a condensate thereof, an emulsifier mixture of an anionic emulsifier and a nonionic emulsifier, and water. The composition undergoes emulsification to form an emulsion. `Emulsification` as defined therein is achieved when the alkylalkoxysilane and the emulsifier are mixed and form an upper layer that is opaque and further where a small amount of water separates to form a lower layer that is more transparent than the upper layer. Suzuki '954 does not disclose particle size of the emulsion. Suzuki '954 does not disclose particle size increase over time.
U.S. Pat. No. 5,746,810 to Suzuki discloses an aqueous emulsion of an alkylalkoxysilane, a surfactant, and water. Suzuki '810 discloses that the emulsion is stable and has particle diameter in the range of 2 to 10 micrometers. Suzuki '810 defines `stable` to mean that after storage, some separation into an opaque layer of silane concentrated emulsion and a colorless transparent layer of water is acceptable when the material can easily be reemulsified. The emulsion has a pH of 7.5-9.
United Kingdom Publication GB 2 301 102 A to Toagosei Co., Ltd., discloses an aqueous emulsion prepared by hydrolyzing a silane selected from the group consisting of alkoxysilanes and alkylhalogensilanes by heating in the presence of an acid catalyst and a small amount of water to form a mixture of the silane and its oligomer, and subsequently emulsifying the mixture with water and an emulsifier. The alkoxysilane has the formula R.sub.n SiR'.sub.4-n, where R is independently selected from alkyl groups, substituted alkyl groups, and aryl groups; n is 1 or 2, and R' is an alkoxy group of 1 to 6 carbon atoms. The emulsifier can be nonionic, anionic, or cationic. The particle size of the emulsion is 1 micrometer or smaller. Emulsions prepared according to Toagosei with particle size larger than 1 micrometer tend to be unstable and liable to phase separation.
U.S. Pat. No. 5,458,923 and U.S. Pat. No. 5,314,533, both to Goebel et al., disclose aqueous emulsions of organosilicon compounds. The emulsion comprise an alkoxysilane, an ionic surfactant, an organosilicon surfactant, and water. The emulsion is stable for weeks at pH 6 to 9. `Stable` is defined as 1. an emulsion having no phase separation and no formation of a layer of cream, or 2. if formation of a layer of cream does occur, the emulsion can be obtained by simple stirring with no loss of effects.
However, none of these patents address the problem of particle size increase with time. This is generally due to a process known as Ostwald Ripening in which the low molecular weight emulsified silane compound has a sufficient solubility in water such that it diffuses from smaller particles through the aqueous phase into larger particles. This results in a net increase in average particle size of the emulsion with time. This can lead to inconsistent behavior or performance of the emulsion in commercial use due to changing properties of the emulsion with age.
Additionally, when an alkoxysilane is used as the silane compound in the emulsion, over time the alkoxysilane can react when it contacts the water phase. The alkoxysilane can undergo hydrolysis and condensation, thereby forming a siloxane and liberating alcohol, which can break the emulsion.
Therefore, an object of this invention is to provide a means to prevent, or minimize, increasing particle size with age; thereby providing the capability to produce stable emulsions of low molecular weight silanes. "Low molecular weight" means a molecular weight (MW) less than 1000.
Particles of increasing size will cream up more rapidly, in accordance with Stokes Law for the rate of creaming of particles in an emulsion. Conversely, if the particles are sufficiently small, the velocity of random particle movement due to Brownian Motion will be sufficient to prevent creaming. The use of additives in the silane compound phase or water phase to decrease the density difference between the silane compound and water to near zero is one technique to minimize creaming. However, this is often undesirable, as it adds to the manufacturing cost of an emulsion and may have detrimental effects on the use of the emulsion in some applications. To reduce creaming, one may also increase the viscosity of the aqueous phase with thickeners such as alginates, as disclosed in U.S. Pat. No. 5,746,810, or with the use of large amounts of emulsifiers relative to the amount of interfacial surface area between the oil particles and the water phase. The use of such large amounts of emulsifier results in the formation of emulsifier structures such as liquid crystals on the particle surface and in the water phase which produces a viscous aqueous phase. Use of excessive amounts of emulsifiers is generally detrimental to the water repellency properties provided by silane emulsions.
Therefore, it is a further object of this invention to produce emulsions of silanes having sufficiently small particle size such that they do not exhibit significant creaming and remain essentially stable in silane concentration with age. To this end it is an object of this invention to provide emulsions having average particle size less than 10 micrometers.
An emulsion will not change in uniformity due to creaming if the emulsion is so concentrated in dispersed oil particles that it is already a cream from top to bottom of the container. The maximum packing of rigid spheres of the same diameter is 74% by volume. Accordingly in theory, as the concentration of silane phase in a polydisperse particle size emulsion approaches or exceeds this concentration, the emulsion becomes quite viscous and unlikely to exhibit non-uniformity due to creaming, as it is already essentially in a creamed state. Due to the viscous, paste-like nature of such emulsions, they are difficult to pump or handle in commercial use.
Therefore, it is a further object of this invention to provide stable silane emulsions with constant particle size that also have low viscosity for ease of handling. The emulsions of this invention have silane concentrations of approximately 65% or less by weight and are easily handled such as by pouring or pumping due to their low viscosity.